Recent investigations demonstrated the existence of potent reflexes controlling arterial pressure in snakes during head-up tilt and graded hemorrhage. The mechanisms involved appear qualitatively similar to those in mammals and birds, but we have yet to assess the components and integrative functions of these control systems in snakes or other reptiles. It is proposed that further research be conducted with the aim of identifying mechanisms controlling arterial pressure and regional perfusion in snakes, especially with regard to the participation of pressure-sensitive reflexes. The specific goals for this next year will employ local and whole body blood flow measurements to assess cardiac shunts and regional adjustments of resistance and blood flow in relation to tilt, hemorrhage and temperature changes in snakes. A major effort will be directed at identifying components of the afferent limb of cardiovascular reflexes. Additionally, comparative morphological studies will examine structural correlates of arterial pressure regulation in different species of snake which differ in habits or habitat.